1. Field of the Invention
The present invention relates to a toner having toner particles, each of which is composed of an inner layer and an outer layer on its outer periphery.
2. Related Art
Initially, image forming devices based on electrophotographic systems were used and spread in the form of office copiers and printers. Currently, a wide product line, ranging from down-sized color printers for personal use to large-scaled ones, called “electrophotographic printers”, has been developed, and its development competition has been increasingly vigorous.
Naturally, toners which are consumables of such devices are changing. Pulverization method toners which are the main stream in the early days have been replaced with chemical toners and polymerization method toners of a uniform particle size distribution and at a smaller particle size. Further, development of these chemical toners and polymerization method toners is not limited to the particle size and its distribution, and has made it possible to design new types of particles by modifying the particle surface. For example, such a toner, described below, is disclosed (refer, for example, to Patent Document 1). Surface-modified toner particles are produced in such a manner that a resinous layer is formed by fusing resinous particles onto toner particles (host body) containing colorants in a resinous phase. Whereby, the existing ratio of colorants which are exposed onto the surface of the toner particle decreases, and thus it is possible to form stable toner images which result in minimal variation of image density, background staining, and color tint during image formation over an extended period at an ambience of relatively high humidity. Further disclosed is the toner below (refer, for example, to Patent Document 2). Particles are formed upon controlling the dispersion state and occupied state of components incorporated in a toner so that effects due to ambient factors such as temperature or humidity are minimized. Subsequently, it is possible to consistently form high quality toner images. Alternatively disclosed is the toner below (refer, for example, to Patent Document 3). Minute particles are added to coagulated particles which are formed by coagulating resinous particles in a resinous particle dispersion so that the minute particles are adhered onto the surface of the coagulated particles. Further, toner particles are prepared by thermally fusing minute particles. Subsequently, it is possible to prepare a toner which exhibit-stable toner properties during the electrophotographic process in which various mechanical stresses are applied onto the surface of the toner particles. Specifically, toner particles in which the surface is covered with particles of desired retention properties have been proposed since early times. However, a number of problems associated with durability, cleaning properties and fixability still remain.
Recently, however, these problems have been overcome and the stage of practical use has started. Recently, waste paper post-processing devices are becoming more wide-spread, and processing such as double-sided printing, bookbinding, saddle stitch bookbinding, and Z-folding are automatically conducted at a high rate. Subsequently, demanded is a toner capable of meeting the demands of the foregoing.
Images composed of toner, which is designed to be fixable at a relatively low temperature, generally remain adhesive until the temperature drops to at most 50° C., whereby in the post-processing device, adhesion and irregular stacking of sheets of paper occur. On the other hand, when a larger amount of particles of high retention properties are employed onto the surface of toner particles, fixability at low temperatures is degraded. At the same time, problems occur in which color images particularly suffer from uneven glossiness. Problems associated with image adhesion and irregular stacking, and low temperature fixability are phenomena which are not compatible with each other, and therefore, it has been assumed that it is too difficult to make them compatible with each other. Furthermore, in order to correspond to belt (film) fixing as well as IH fixing which is receiving attention as a recent energy saving fixing, method demanded is fixability at a relatively low pressure, as well as an increase in the fixable temperature range which does not result in off-setting even though non-uniformity of temperatures occurs to fixing members.
(Patent Document 1)
Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2002-116574 (paragraph 0005, etc.)
(Patent Document 2)
JP-A No. 2002-351142 (paragraph 0016, etc.)
(Patent Document 3)
JP-A No. 10-26842 (paragraph 0012, etc.)